Guys,
I don't understand why there are folks from the US talking about electrical system Earthing outside of the US.
Don't get me wrong, but these two countries use two totally DIFFERENT methods of Earthing.
I also have no idea why dsk is referencing the US NEC when it has no jurisdiction in Norway.
Earthing or Grounding, or whatever you call it wherever you are, is vital to the safe operation of an electrical installation.
Good earthing makes sure that the protective devices in your switchboard operate within 0.4s of a fault occurring between the line and neutral conductors of any circuit.
Further to this, an RCD/GFCI needs to disconnect a faulty circuit/appliance within 300mS should there be a fault to Earth/Ground from a Line conductor.
I also ask this question of any Qualified Electrician here, do you own test equipment to test an entire installation before the power is connected to it?
By this I mean, a Megohmmeter, an Earth Loop/PSCC Tester and an RCD/GFCI tester?
If you don't, you are opening yourself up to so much liability if you do not test things before livening.
If you don't know how to use this sort of test gear, I would suggest you start learning now.
While the US does not have "self-certification" by Electricians, you should always "own" a job you do,
this is what I do here in New Zealand as an Inspector.
